Optimint Hardhat Implementation

Optimint is a gas-optimized ERC721 reference implementation that's based on OpenZeppelin Contracts, and requires only 1 SSTORE operation per batch-mint. Please see the benchmarks file to compare gas-usage.

Note: We use OpenZeppelin Contracts as a base, but these optimizations can be utilized in other implemenations.

Optimized Gas

Optimint gas optimization is achieved by storing owner addresses inside token identifiers, instead of writing them to storage:

uint tokenId = (uint(owner) << x) | N;
ownerOf(tokenId) = address(tokenId >> x);

We commit a token owner's address to storage only after the token's been transferred for the first time:

ownerOf(tokenId) = _owners[tokenId];

Limitations

• Total supply should be limited based on the ERC721Inventory.BALANCE_BITSIZE setting. For example, if it's set to 16, then supply should be limited to type(uint16).max. The ERC721Supply extension is provided to enforce this limitation, and its _maxSupply method can be overridden to enforce a lower one.
• The maximum number of tokens a single address can mint is limited based on ERC721Inventory.SLOTS_PER_INVENTORY. It's set to 232 by default, but may change when updating other settings. You can enforce a lower limit by overriding ERC721._maxMintBalance.
• Enumerability isn't trivial.

Enumerability

This repo includes an ERC721Enumerable implementation that can be used to provide on-chain enumerability. While most interactions remain unaffected, gas usage on mint is a little higher than ERC721A's. See benchmarks for more details.

Benchmarks

You can run the benchmarks locally:

npx hardhat run scripts/benchmarks.js

Note: Benchmarks may take a minute to complete.

Contributations

All contribuations are welcome! Feel free to open a PR or an issue.

License

MIT license. Anyone can use or modify this software for their purposes.